This invention relates to a trolley for track systems with essentially right-angled intersections, with raisable and lowerable rollers on the trolley for alternatively engaging with one pair of the intersecting pairs of tracks.
This invention is especially applicable to track systems with tracks having a circular cross-section that are largely sunk into the ground, as described in DE 43 18 383 CI. These types of track systems can e.g. be laid in a works hall without creating any major obstacle to walking or driving over the floor of the hall. They also have a very high load-bearing capacity, making them particularly suitable for transport work in industrial halls.
In order to make use of the entire surface area of the hall, the tracks usually have to be laid in a grid with right-angled intersections. The transition from one pair of tracks to another pair of tracks intersecting at a right angle is achieved by raising the rollers associated with the first pair of tracks, and simultaneously lowering, in relation to the trolley, the rollers on the trolley associated with the intersecting pair of tracks. This ensures that only the rollers associated with the intersecting pair of tracks engage with these latter tracks. Given that in certain circumstances, the said changeover process has to be effected with high or very high loads, it has proved difficult to create a hard-wearing, durable changeover device that is nonetheless as simple as possible and designed to ensure that the changeover process can be carried out as quickly as possible.
The invention is therefore based on the task of creating a trolley of the above-mentioned type with a changeover device for the rollers which allows the rollers to be raised and lowered virtually simultaneously and with relatively little application of force.
According to the invention, this task is solved by a trolley of the above type which is characterized in that an actuator is provided for simultaneously raising, in relation to the trolley, the rollers which engage with one pair of tracks and lowering, in relation to the trolley, the rollers which engage with the intersecting pair of tracks.
The changeover system according to the invention therefore comprises only one actuator, e.g. a hydraulic cylinder, a spindle drive or similar.
The trolleys of the type in question here are generally equipped, in a quadratic arrangement overall, on all four sides and in the vicinity of the ends of these sides, with rollers or roller groups comprising two or three rollers.
According to the invention, these rollers or roller groups are preferably mounted on the underside of the trolley by means of suspension arms, and more specifically in such a way that a pulling or pushing force in the direction along the side edges causes the suspension arms to pivot, thereby raising or lowering the rollers or roller groups. This means that the vertical adjustment of the rollers or roller groups can be effected by exerting an appropriate pushing or pulling force on the roller groups, e.g. from a position in the middle of each of the side edges.
The central actuator preferably acts on two intersecting shafts which are mounted on the trolley, are coupled via a bevel gear system and each extend from side-middle to side-middle, i.e. end up between the two rollers or roller groups on the four sides of the contour of the trolley. Advantageously attached to these ends there are double levers, each end of which is pivotably connected to a rod which is pivotably connected by its other end to a roller or roller group. By rotating the shafts and pivoting the double levers correspondingly, a pulling or pushing force can be exerted via the rods in the direction of the rollers or roller groups. The pulling or pushing force lowers or raises the rollers in relation to the trolley, the rollers being, as already mentioned, pivotably mounted on the trolley by means of suspension arms.
The suspension arms of the rollers or roller groups and the double levers of the shafts are preferably arranged so that when the rollers or roller groups are lowered, the suspension arms point vertically downwards and the double levers assume a horizontal position. In this way the suspension arms are subject to upwardly directed push along their longitudinal direction and any deflected lateral forces which might act on the suspension arms under heavy loads are absorbed by the double levers in their longitudinal direction. Both stress directions are extremely advantageous from the kinematic point of view, and, in particular, prevent the drive together with the shaft system from having to exert significant holding torque in order to absorb the stress of the lowered rollers.
There is another advantage to said arrangement of the suspension arms and the double levers. This has to do with the fact that the rods disposed between the double levers and the rollers or roller groups are not displaced linearly, but execute circular movements. Because of the said arrangement, the horizontal component of the rods is relatively large at the beginning of the lowering movement as the rollers or roller groups are lowered onto the tracks, whilst the horizontal component then becomes smaller and smaller as the double levers rotate. On the other hand, the vertical component of the rollers or roller groups is also relatively large at the beginning of the lowering movement of the roller groups or rollers, whilst it decreases progressively towards the end of the lowering movement. The result is that when the rollers or roller groups are changed, the lowering movement of the rollers for one of the pairs of tracks precedes the raising movement of the rollers of the other pair of tracks. This means the trolley is supported by the new rollers relatively quickly, so that it loses virtually no height when the rollers are changed. Having to lift the trolley up again after any loss of height would require enormous force and an actuator of a corresponding size if the trolley were heavily loaded.